Ed takes a look at how a 3D printer has simplified his projects by producing some peculiar objects. Once you see how he puts his printer to use, you’ll surely want to add one to your workspace.
Some projects begin with sketches of the circuitry to implement a function, others by doodling the case that must contain the circuit, and, alas, some require a miracle to fit large components into a minuscule volume. In the early days of electronics, cases were relentlessly rectangular, because that’s what machine shops could produce. Today’s products have smoothly flowing curves and stylish designs, to the extent that you (or the mechanical engineers on your team) may devote as much effort to the container around your electronics as to the circuitry and software within.
While the “style” of the cases for my homebrew projects tends toward the utilitarian, they have become much less boxy in the last few years, because my 3D printer can produce complex objects with minimal machine-shop effort. Sometimes a rectangular prism has the proper shape, but now I can generally build a part with exactly the right features, no matter what it looks like.
In this column, I’ll explain how a 3D printer’s ability to produce arbitrary shapes has improved the gadgets I produce in my shop. On Circuit Cellar’s article code and files webpage, the downloadable file for this column includes links to the OpenSCAD programs that generate the solid models and the dates of previous columns that describe the circuitry in more detail.
WRAPPING THE ELECTRONICS
The colorful plastic case in Photo 1 contains two PCBs: a slightly modified Byonics TinyTrak3+ GPS encoder and a board I designed to combine that GPS data with voice audio for use with an amateur radio HT. The case latches onto the HT’s back, replacing the lithium battery pack. The short cable from the lump on the HT’s side connects its external speaker and mic jacks to my circuitry.
After machining several awkward, unsatisfactory, and painfully ugly polycarbonate plastic boxes, I bought a 3D printer in late 2010 specifically to build a better case. After devoting half a year to improving the 3D printer and a year to improving my solid modeling skills, I had a workable design.
The case includes metal parts for more strength than the 3D-printed plastic can provide. For example, the sliding brass bar just visible near the top secures the entire assembly to a pair of bosses cast into the HT’s frame. Those radios with their backpacking circuit boards have traveled thousands of miles on our bikes during the past five years!
However durable the plastic may be, most of the cases I build in my shop have shorter lifetimes, as part of an investigation of an interesting phenomenon. For example, the solid model in Photo 2 shows the housing for a gamma-ray detector based on a Cold-War era ionization chamber that I built to determine if the chamber still worked. The green latticework hexagon represents the copper-clad circuit board, with copper foil lining the hexagonal box to form a solid electrostatic shield. The plastic structures provided electrical isolation between the outside of the ionization chamber at +24 V and the copper ground plane of the circuit board, support for the circuit board and cap, and a ring at the bottom of the chamber to lift a protruding solder seal off my workbench.
Machining those shapes from solid plastic would be difficult, but it’s a straightforward 3D printer operation, after I correctly figured the relationships among all the dimensions. “Engraving” labels into the cap added very little effort and minimal production time.
Unlike complex cases for complete circuit boards, the black plastic fixture in Photo 3 aligned 5 mm LEDs in front of the large BNC-output photodiode to measure their light output as a function of current. The orange pegs hold the bottom section in place, with foam padding capturing the LED and ensuring a light-tight seal around its leads extending outward through the straight channel. The four neutral-density filter disks help calibrate the photodiode’s response to intensity variations.
Given the fixture’s simple geometry, I could build it with my lathe and milling machine, even without CNC. A 3D printer produces equivalent results, without the need to machine all the related parts every time. Even subtractive CNC machining requires manually clamping and re-clamping while shaping various surfaces.
The ability to make a new object that’s similar to a previous one became vital for the test fixtures I use to measure lithium battery capacity. For reasons best known to camera manufacturers, every single lithium battery has slightly different external dimensions, contact locations, and keying features: no holder will accept more than one battery.
The cutaway solid model in Photo 4 shows the internal structures of the holder I designed for the Sony NP-BX1 battery used in the HDR-AS30V action camera. The small features in the rectangular compartment ensure the battery fits snugly in the correct orientation and the two small holes in the top surface, between the contact pins, align a cap extending over the battery compartment to hold the battery into place. The stepped diameters along the contact pin hole accommodate pin flanges, a helical compression spring, and a plastic ring surrounding the test leads to preload the spring.
The deep contact pin holes require reaming to final size, because the printer can’t produce horizontal holes with good tolerances. On the other hand, all the other dimensions are accurate enough that “final assembly” for each holder consists of gluing the cap, soldering test leads to the contact pins, then clamping and gluing the rings in place behind their springs. Creating a holder for Yet Another Battery requires tweaking the dimensions to generate a slightly different solid model, then working on another project for an hour while the printer builds the parts.
TOOLS FOR THE MAKING
The speed knobs in Photo 5 represent one step of the recursive descent that often happens in my shop: building a special-purpose tool to simplify building something else. I’d been adjusting those chuck jaws with a single hex key, until I read an article showing how four knurled steel speed knobs simplify the process, whereupon I created a parametric solid model of a knob suitable for 3D printing. Although I’ll grant that red PLA isn’t nearly as pretty as knurled steel or brass, they work just fine for my needs and the chuck doesn’t seem to mind.
The business end of each wrench holds a press-fit section of an ordinary 5/32 inch hex key. Despite 3D printing’s reputation for being able to produce any shape, plastic isn’t well-suited for tools that must withstand more than trivial amounts of torque or force. Metal inserts provide far more strength with much better tolerances, even if they require an additional assembly step.
Modifications of that solid model produced tommy bar handles, cap-screw knobs, and wrenches for sewing machine adjustments. They may not be essential, but they’re nice to have and easy to make.
On my electronics bench, a stereo zoom microscope sees almost continuous use while I work with tiny components and small parts. After designing an eyepiece adapter for a small USB camera, I needed a better way to position objects in the microscope’s field of view: my eyes are much more accommodating than the camera!
A surplus micromanipulator provided the black-and-silver axis slides in Photo 6, fixed in a completely different layout from its OEM application. The cyan PETG parts rearranged the slides to extend the aluminum stage under my microscope’s objective lenses and put the knobs near my right hand. As you might expect, the long plastic arm holding the XY slides isn’t nearly as rigid as the original steel structure, but gentle knob-twisting still moves the stage in minute increments along all three axes.
Printing those three blocky parts, each with several holes sized for the original mounting screws, required about four hours, plus a few minutes to assemble the parts. I tweaked my first design to produce the version you see here, which I certainly wouldn’t have done if that required another four hours of hands-on machine work.
The black rings in Photo 7 fit around the finger-grip flange on the probes for my HP oscilloscope. The simple shape required only a few minutes to design and print, so repairing a cracked flange barely interrupted the project on my workbench. The result, however, clearly contrasts the surface finish of the 3D printed parts with the glossy injection-molded probe tip.
Commercial 3D printers using different processes, ranging from laser sintered powders to optically cured liquids, can produce finer surface finishes, with sometimes severe tradeoffs in other mechanical properties. If your application requires a smooth surface finish, you should plan for hand-finishing operations that may include epoxy coatings, high-build paint primers, and sanding / polishing. The results can be spectacular, but you must regard the 3D printed object as a substrate for further work, rather than a rapid-turnaround finished part.
If I cared more about the surface properties of my repair parts, I suppose using a light-colored plastic for these rings, rather than the black PLA I had in the printer, would be a step in the right direction. Conversely, you could print sets of customized color-coded rings to identify all your probes, if you have far more probes than I do.
PUTTING IT ALL TOGETHER
Over the years, I’ve filled a box labeled “Hollow State Electronics” with an assortment of vacuum tubes, lamp bulbs, and interesting glass objects. I recently began turning those treasures into table decorations only a techie could love, with the 21HB5A beam power tetrode in Photo 8 as a particularly nice example. Although these lamps seem to be electronic projects, it turns out that 3D printing makes them possible.
A programmable RGB LED (a knockoff of Adafruit’s Neopixel line) illuminates the tube’s bottom and another lights its top, with an Arduino in the base calculating the slowly changing colors from three sine waves with mutually prime periods. The shiny platter, harvested from a 3.5 inch hard drive, reflects the tube’s lower mica insulator and holds the parts together. I was pleasantly surprised to discover how well a pair of RGB LEDs can light a dark room.
In their original circuits, vacuum tubes operated from dangerously high voltages and dissipated enough power to require high-temperature ceramic or Bakelite sockets. In their new application, the tubes remain completely inert and their low-voltage LEDs and microcontrollers dissipate barely 250 mW. Despite that, some onlookers think the tubes’ internal glow comes from ionized gases!
Because the sockets no longer provide electrical connections and need not withstand the heat of orange-hot filaments, a 3D printer can produce the intricate shapes shown in Photo 9. The lower LED press-fits into the central hole, just under the tube’s base, where it illuminates the tube’s internal structure.
Bottom-up illumination works well with “modern” all-glass tubes, but older octal base tubes, introduced in the mid-1930s, have an opaque Bakelite base. The white PETG fixture in Photo 10 holds the tube base in a machinist’s V-block clamp with the end of the glass envelope resting on a plastic pad, so that my Sherline milling machine can remove the central post to let light into the base. A rib on the post ensured proper orientation in the original socket, a feature that no longer matters.
The tube’s evacuation tip, a thin glass tube melted to seal the tube after pumping out its air, may extend into the post’s hollow core. After milling away the post’s end, you must determine the tip’s position before proceeding. The PETG fixture and plastic pad let me unclamp the tube, find the evacuation tip, and reclamp the tube in the same position.
The 3D printed fixture in Photo 11 holds 3.5 inch hard drive platters on the milling machine’s table. The small black dots along the front edge mark reference points 50 mm from the disk’s center, so that I can set the coordinate offsets and drill several disks in succession with a short CNC program. Plastic film on the disks prevent surface scratches from the clamps and swarf.
Tube designed to handle particularly high voltages, such as the multi-kilovolt rectifiers in color televisions, required a plate electrode connection isolated from the socket. A terminal atop the envelope, attached to a wire sealed through the glass, accepted a heavily insulated cap at the end of a wire from the chassis. Although the 21HB5A tube in Photo 8 never had a plate cap, I adapted the idea to bring power and data to the upper LED through a braided sleeve, with a thin ring of opaque epoxy holding the 3D-printed cap to the glass envelope.
A pair of threaded brass inserts in the socket anchor the two screws holding it to the platter. After installing the socket with its base LED on the platter, I plug the tube into the socket, attach its plate cap, thread the braid through the platter, then solder the wire to the base LED. The notches in the bottom of the sockets, barely visible in Photo 8, capture the wires from the cap and Arduino to reduce strain on the PCB’s solder pads.
The base shown in Photo 12 holds the Arduino Pro Mini microcontroller and its outboard USB-to-serial adapter or an Arduino Nano with its built-in USB converter. As with the tube socket, brass inserts in the four posts anchor the screws through the hard drive platter. The CNC-drilled platter holes match up perfectly with inserts pushed into the 3D printed parts: final assembly never requires abrasive adjustment.
The media seems to emphasize a consumer-grade 3D printer’s ability to convert downloaded solid models into licensed tchotchkes in the privacy of your own living room. I doubt that will ever become a viable business, but being able to build exactly the components, parts, fixtures, and tools I need for my projects certainly justifies the 3D printer in my shop.
Even though vacuum tubes haven’t been manufactured for decades (with a few notable exceptions), they’re neither rare nor expensive. A few moments browsing the eBay listings should turn up a wide variety of glass sculptures, as well as RGB LEDs and microcontrollers. Maybe that will justify a printer in your shop, too.
 E. Nisley, “KG-UV3D GPS+Voice Interface: APRS Bicycle Mobile,” 2012, https://softsolder.com/2012/09/11/kg-uv3d-gpsvoice-interface-aprs-bicycle-mobile/.
 ———, “Victoreen 710-104 Ionization Chamber: Revised Fittings,” 2015, https://softsolder.com/2015/09/07/victoreen-710-104-ionization-chamber-revised-fittings/.
 ———, “ LED + Photodiode Test Fixture,” 2013, https://softsolder.com/2013/05/23/led-photodiode-test-fixture/.
 ———, “ Sony NP-BX1 Battery Test Fixture,” 2014, https://softsolder.com/2014/02/04/sony-np-bx1-battery-test-fixture/.
 ———, “Sherline Four-Jaw Chuck Speed Wrenches: 3D Printed Edition,” 2013, https://softsolder.com/2013/12/12/sherline-four-jaw-chuck-speed-wrenches-3d-printed-edition/.
 ———, “Microscope Stage Positioner,” 2016, https://softsolder.com/2016/01/18/microscope-stage-positioner/.
 ———, “HP Scope Probe Flange Repair: Improved Spares,” 2013, https://softsolder.com/2013/12/03/hp-scope-probe-flange-repair-improved-spares/.
 ———, “Vacuum Tube LEDs: Fully Dressed 21HB5A,” 2016, http://softsolder.com/2016/09/20/vacuum-tube-leds-fully-dressed-21hb5a/.
 ———, “ Vacuum Tube LEDs: Ersatz Tube Sockets,” 2016https://softsolder.com/2016/02/10/vacuum-tube-leds-ersatz-tube-sockets/
 ———, “Improved Octal Tube Base Clamp,” 2016, http://softsolder.com/2016/10/04/improved-octal-tube-base-clamp/.
 ———, “Hard Drive Platter Drilling Fixture,” 2016, http://softsolder.com/2016/09/14/hard-drive-platter-drilling-fixture/
 ———, “Vacuum Tube LEDs: Hard Drive Platter Base,” 2016, https://softsolder.com/2016/09/13/vacuum-tube-leds-hard-drive-platter-base/.
E. Nisley, “Building Boxes,” Circuit Cellar 173, 2004.
PUBLISHED IN CIRCUIT CELLAR MAGAZINE • JANUARY 2017 #318 – Get a PDF of the issueSponsor this Article